Portable spectrometer

ABSTRACT

A portable spectrometer device includes an illumination source for directing at a sample, and a tapered light pipe (TLP) for capturing light interacting with the sample at a first focal ratio and for delivering the light at a second focal ratio lower than the first focal ratio. A linearly variable filter (LVF) separates the captured light into a spectrum of constituent wavelength signals; and a detector array, including a plurality of pixels, each of the plurality of pixels disposed to receive at least a portion of a plurality of the constituent wavelength signals provides a power reading for each constituent wavelength. Preferably, the TLP is lensed at one end, and recessed in a protective boot with stepped inner walls. The gap between the TLP and LVF is minimized to further enhance resolution and robustness.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority from U.S. Provisional PatentApplication Nos. 61/725,923, filed Nov. 13, 2013 and 61/784,811, filedMar. 14, 2013, which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a portable spectrometer, and inparticular to a robust, high-performance, portable spectrometerrequiring minimal power and size.

BACKGROUND OF THE INVENTION

Over the last decade NIR spectroscopy has increasingly developed to anindispensable analytical tool for production and quality control in thepharmaceutical industry. Qualitative NIR investigations are frequentlyapplied in the identity control of incoming raw materials, whereasquantitative analysis of the final product is an important step in thepharmaceutical process chain. However, the majority of pharmaceuticalanalyses is still performed by taking a sample from the production siteand transporting it to a remote quality control laboratory. This delaybetween sampling and availability of results limits the frequency ofanalysis and the optimization of the production line. Thus, novelportable field instrumentation capable of performing a rapid at-line orin-line analysis of the process can be considered as a key tool toadvance the effectiveness of the pharmaceutical industry.

Older versions of compact spectrometers, such as the ones disclosed inUnited States Patent Publication 2012/0188541, published Jul. 26, 2012to Ocean Optics, Inc, and 2005/0007596, published Jan. 13, 2005 in thename of Wilks Enterprise, Inc. attempt to minimize their footprint byproviding a series of optical path folding mirrors. Unfortunately,folding mirrors require extensive alignment procedures duringmanufacture, and do not provide a very robust structure for field-usedevices resulting in low or unpredictable performance.

Historically, light conduits, light pipes or light transfer conduitswere used for light beam shaping or light redirection applications.Examples are display engine technologies for displays or frontprojection television applications, such as those disclosed in U.S. Pat.Nos. 7,252,399 and 7,033,056; and United States Patent Application No.2006/0044833. U.S. Pat. No. 6,420,708, issued Jul. 16, 2002 to Wilks etal, discloses a spectrum analyzer, which includes a rectangular lightpipe or crystal for transmitting light to a sample, but not for shapingthe reflected light for delivery to a filter.

U.S. Pat. Nos. 6,473,165; 7,006,204; and 7,184,133 relate to automatedverification systems in which the reflectance of two separate beams oflight at two different angles of incidence reflected off of an opticalinterference security feature are measured and compared. A convergingtapered light pipe is disclosed for collecting and concentrating light.

An object of the present invention is to overcome the shortcomings ofthe prior art by providing a high-performance, robust, portable,low-power spectrometer including a broadband light source and detectorarray for use in an in-the-field sample testing device.

SUMMARY OF THE INVENTION

Accordingly, the present invention relates to a portable spectrometerdevice comprising:

an illumination source for directing light at a sample;

a tapered light pipe (TLP) for capturing light interacted with thesample at a first focal ratio and for delivering the light at a secondfocal ratio lower than the first focal ratio;

a linearly variable filter (LVF) for separating the captured light intoa spectrum of constituent wavelength signals; and

a detector array, including a plurality of pixels, each of the pluralityof pixels disposed to receive at least a portion of one of theconstituent wavelength signals providing a power reading for eachconstituent wavelength;

wherein the TLP includes a first smaller end for positioning adjacent tothe sample, a second wider and taller end adjacent to the LVF, andsidewalls diverging from the first end to the second end for mixing andspreading the light across the LVF.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail with reference to theaccompanying drawings which represent preferred embodiments thereof,wherein:

FIG. 1 a is a schematic diagram of the spectrometer system in accordancewith the present invention;

FIG. 1 b is a perspective view of the spectrometer of FIG. 1 a in auser's hand;

FIG. 1 c is a perspective view of the spectrometer system of FIG. 1 a;

FIGS. 2 a and 2 b are side views of two different embodiments of theportable spectrometer of FIG. 1 a;

FIG. 3 is a top view of one of the light sources of the portablespectrometer of FIG. 1 a;

FIG. 4 is a top view of a housing of the portable spectrometer of FIG 1a;

FIGS. 5 a, 5 b and 5 c are isometric, side and top views, respectively,of the tapered light pipe of the spectrometer of FIG. 1 a;

FIG. 6 is a plot of transmission vs wavelength for a spectrometer withand without a TLP;

FIGS. 7 a and 7 b illustrate incoming and outgoing ray bundles from astandard TLP and a lensed TLP, respectively;

FIG. 8 is a plot of transmission vs wavelength for a spectrometer withand without a lensed TLP;

FIG. 9 is an isometric view of a TLP boot of the portable spectrometerof FIG. 1 a;

FIGS. 10 a and 10 b are plots of response vs wavelength for aspectrometer with and without the TLP boot, respectively, of the presentinvention;

FIG. 11 is a side view of the LVF of the portable spectrometer of FIG. 1a;

FIG. 12 is a schematic view of the LVF and detector array of theportable spectrometer of FIG. 1 a;

FIGS. 13 a and 13 b are plots of response vs wavelength for aspectrometer with a 750 um gap and with a 200 um gap, respectively,between LVF and detector array of the present invention

FIG. 14 illustrates a side view of a LVF and detector array structure inaccordance with the present invention;

FIG. 15 is a schematic illustration of a wireless spectrometer system inaccordance with the present invention; and

FIG. 16 is a schematic illustration of an alternative wirelessspectrometer system in accordance with the present invention.

DETAILED DESCRIPTION

With reference to FIGS. 1 a, 1 b, 1 c, 2 a and 2 b, a compactspectrometer 1, in accordance with the present invention, is a verysmall, e.g. less than 5 pounds, preferably less than 2 pounds, morepreferably less than 0.5 pounds, and ideally less than 100 g withoutbattery, compact, e.g. less than 6″×6″×2′, preferably less than6″×3″×1″, and more preferably less than 4″×2″×0.5″, low-cost hand-heldspectrometer built around a light filter 2, mounted on a broadbanddetector array 3, e.g. more than 500 nm, preferably more than 600 nm andmost preferably more than 700 nm wide, such as an indium galliumarsenide (InGaAs). The light filter could be any form of spectrometer,e.g. diffraction based, phase holographic, frustrated total reflection(FTR) or linearly variable filter (LVF) based instruments, that requiresa specified input cone angle to function, but an LVF is preferred.

The LVF is a dielectric thin-film Fabry-Perot bandpass filter depositedusing energetic processes, well known to produce stable and reliableoptical components. The filter coating in the LVF is intentionallywedged in one direction. Since the center wavelength of the bandpassfilter is a function of the coating thickness, the peak transmittedwavelength varies continuously along the direction of the wedge. The LVFis typically fabricated from inorganic materials, such as SiO2 andTa2O5, produced by ion-assisted physical vapor deposition techniquesresulting in dense coating with high reliability and stability.

Ideally, the spectrometer 1 is entirely USB-powered, i.e. thespectrometer is powered by 2.5 W or less, but battery power with awireless connection is within the scope of the invention, as will bedetailed hereinafter. A control system 4, comprised of a processor andsuitable non-transitory memory, includes a suitable USB connector forreceiving a USB cord 6, enabling the transfer of data between thecontrol system 4 and a host controller device 7, e.g. laptop, notebook,notepad or pda, ideally housed in a protective cover 8. One or moreself-contained light sources 12 activated by switch 10 are used todirect light onto a sample 15 so that the diffusely reflected,transmitted or otherwise interacting radiation will be captured by alight collection optic, e.g. a tapered light pipe (TLP) 11, for deliveryto the light filter, e.g. LVF 2.

In order to minimize the size of the spectrometer 1 and the operatingpower consumption, while maintaining robustness and high performancemany problems had to be solved including: 1) making the light path asefficient as possible; 2) using the TLP 11 in the train instead offibers, 3) placing the LVF 2 close to the detector 3 to minimize theoptics required; 4) leaving the detector array 3 uncooled, to avoid thepower requirement of a TE cooler; and 5) providing light source(s) 12that consume as little power as possible, but still provide broadbandillumination, e.g. in the IR region.

The spectrometer 1, in accordance with the present invention, consumesless than 2.5 W of power when operating, even when the light sources 12are comprised of two or more lamps. For near infrared, the light sources12 are preferably comprised of one or two onboard incandescent lamps,e.g. vacuum tungsten lamps, that provide broadband illumination, e.g.over 500 nm, preferably over 700 nm, most preferably over 1000 nm acrossthe active range of the instrument, e.g. for the NIR in the 900 nm to1700 nm range or in the 900 nm to 2150 nm range. One lamp 12 issufficient; however, two lamps 12 adds more light for the sample tointeract with, hence shorter integration times. There is a practicallimit; however, space constraints and USB or battery power limits.

With reference to FIGS. 2 a and 2 b, there are typically twoconfigurations for the light sources 12. In one configuration, thesample 15 is illuminated at an acute angle from normal to the sample 15,e.g. 45° from a longitudinal axis LA of the TLP 11, with relativelycollimated light from one, two or a plurality of light sources 12, andwith an end of the TLP 11 disposed equidistant between each lamp. Thelongitudinal axis LA of the TLP 11 is perpendicular to the substrate ofthe LVF 2 and the detector array 3. In the other arrangement, the sample15 is flood illuminated. In both arrangements, the receiving end of theTLP 11 is disposed to receive light at substantially normal incidencefrom the sample 15, i.e. along the longitudinal axis LA. The lightsources 12 are disposed to exclude specular reflection from the sample15. The 45° illumination diffuses reflectance or transflectancemeasurements. Each light source 12, ideally comprises a lens tippedvacuum tungsten lamp for creating a 5 mm, preferably 3 mm or less, spoton the sample 15. With reference to FIG. 4, the light sources 12 and theend of the TLP 11 are ideally recessed in a housing 20, which extendsoutwardly from a main body of the device 1. The housing 20 has anopening covered by a transparent, e.g. sapphire, protective window 21through which the light is projected onto the sample 15, and thereflected light is captured by the TLP 11. The housing 20 protects thelight sources 12 from damage, and prevents stray light from externalsources from entering the end of the TLP 11. Both reflectance andtransmission modes, in which the sample 15 is placed between the lightsource 12 and the TLP 11, are possible, as illustrated in FIGS. 2 a and2 b, respectively.

The concept of a small portable body, also could include, but notlimited to, a small screen on the back for viewing spectra, a simplepoint-and-shoot interface, a battery, a memory card for storing spectra,a computer interface, a flash or onboard illumination source, and aframework for building, loading and using onboard “applications” forpost-processing the data.

The first embodiment of the light sources 12 incorporated the use of twolens tipped vacuum tungsten lamps to present intense NIR light to thesample 15. Ideally, the lamps are orientated so that light would strikethe sample 15 at an acute angle, e.g. 45°, from normal to the sample,and specular reflections would reflect into the opposite lamp. Ideally a3 mm diameter spot is created on the sample 15. No direct specularreflection would, under normal conditions, enter into the entranceaperture of the TLP 11. This is still a viable illumination condition,but has one drawback, i.e. the two projected beams coincide at onelocation with a “measurement depth of field” of ˜500 μm. Many, if notmost, NIR measurements measure light from the surface as well as withinthe sample, i.e. penetrating depth can be as great as 10 mm in somecases. This illumination, while excellent for controlling specularreflection, can create variable transflectance results. If the sample 15is being measured at its surface only this is a viable illuminationarrangement.

The light sources 12 of the alternative embodiment incorporates floodillumination with non-directional lamps. The flood illumination bathesthe sample 15 with non-collimated light that mitigates the “measurementdepth of field” problem, i.e. up to 10 mm for transflectancemeasurements, not just surface measurements. Flood illumination is alsoable to deliver more NIR light flux to the sample 15 being measured. Theextra degrees of freedom come at a price of needing to control parasiticspecular light from the front protecting window 21 of the spectrometer1. This is achieved with the use of a terraced boot 25 (See FIG. 7) thatstrictly defines the field of view as seen by the entrance aperture ofthe TLP 11. Mitigation of unwanted light from the lamps 12 into the TLP11 is achieved by position of the lamps 12 with respect to the entranceaperture of the boot 25, how close the boot 25 is from the rear surfaceof the window 21, how thick the window 21 is and coatings applied to thewindow 21 to minimize specular reflection.

The TLP 11 provides light collection optics designed to present spectrallight energy at any desired wavelength, i.e. reflected from a lambertianscattering surface or transmitted translucent surface of the sample 15,to the input surface of the LVF 2 for transmission to detector array 3.In order for the filter/detector array assembly ⅔ to operateefficiently, light entering the LVF 2 needs to have maximum acceptanceNA of 0.2 or smaller. To achieve an acceptable NA the output radiationpattern collected from the sample 15 being measured requires a lens or atapered light pipe. The tapered light pipe 11 can be solid, e.g. SchottN-BK7 glass, or hollow in construction, depending on the spectralengines or spectrometers operating parameters. The taper angle of theTLP 11 can be optimized for reflection or transmittance type samplingand/or optical path length. The TLP 11 can have a reflective coatingapplied for either the hollow or solid designs or without coatings.Tapered and non-tapered light pipes may or may not have lightrecirculation properties to increase signal from the sample.Spectrometer or spectral sensory will dictate the wavelength region ofinterest and ultimately govern light pipe design.

The tapered light pipe (TLP) 11, a specific example of which isillustrated in FIGS. 5 a, 5 b and 5 c, captures light at a first smallerend from lambertian light sources, i.e. reflections of the lamps 12 froma highly scattering surface, e.g. solid or liquid samples 15, at a firstfocal ratio, e.g. f/1, and cone angle, e.g. between 20° and 40°, buttypically about 30°, and mixes, spreads out and reshapes the reflectedlight into the required lower focal ratio f/3, i.e. cone angle of about10° or less, required for better operation by the LVF 2 within thespectrometer 1. The tapered light pipe 11 acts as a disperser and lightreshaping device with diverging sidewalls, e.g. four, that spreads outthe light and enables the electromagnetic waves to pass from a secondlarger end, e.g. taller and wider, through the LVF 2 from the lambertianilluminated surface. Accordingly, the TLP 11 enables the spectrometer 1to sample light from a relatively large area, collecting light from anylambertian scattering surface, contrary to competing technologies, whichgenerally collect light with fiber optic that originates from a smalllocalized area. Moreover, the TLP 11 mixes and spreads out the light toaccommodate the size of the LVF 2 and the pixels in the pixel array 3.The LVF 2 can then be optimized to accept light that deviates less than10° from a normal, i.e. to the coating surface and/or the LVF substrate,thereby greatly improving resolution and performance.

The focal ratio is the ratio of the focal length of the telescope to itsaperture. It's calculated by dividing the focal length by the aperture.For example, a telescope with a 2032 mm focal length and an aperture of8″ (203.2 mm) has a focal ratio of 10 (2032/203.2=10) or f/10.

The TLP 11 is a light beam steering/reshaping device that employscompound angles to slow an optical light cone from a first (fast) focalratio, e.g. f/1, to a second lower (slower) focal ratio, e.g. f/3, andenable the LVF 2 to spectrally perform. This is accomplished bycontrolling the aspect ratio of the entrance and exit apertures of theTLP 11. The length of the TLP 11 needs to be long enough to achievesufficient mixing of the light and achieve the proper (slower) focalratio at the exit aperture. FIG. 6 illustrates the difference intransmission, i.e. much less, and wavelength, i.e. much broader, for aspectrometer with or without the TLP 11.

The entrance aperture of the TLP 11, closest to the lamps 12, has asmaller opening of 1.5 to 2.5 mm (preferably 2 mm +/−0.1 mm)×0.4 mm to0.6 mm (preferably 0.5 mm +/−0.1 mm. The exit aperture, proximate theLVF 2, has a larger opening 6 to 7 mm (preferably 6.6±0.1 mm) wide and0.75 to 1.25 mm (preferably 1.0 ±0.1 mm) long. The length of TLP 11 is15 to 25 mm (preferably 20±0.3 mm) tapering in both height and width tothe entrance end. Accordingly the taper angle is between 6° and 7° perside from the longitudinal axis, with a total of 12° to 13° for thewidth, and between 0.5° and 1° per side from the longitudinal axis, witha total of 1° to 2° for the height.

Unfortunately, as a result of the TLP 11, the ray bundles exiting theTLP 11 are no longer normal to the LVF 2, i.e. they tilt up to 6° oneither end of the detector array 3 (See FIG. 7 a). As a result two badeffects occur, which are worse at the ends of the detector array 3: 1)there is a downshift in center wavelength; and 2) there is a broadeningof the bandwidth (resolution). The shorter, broader plot in FIG. 8illustrates the performance of a spectrometer with a flat TLP 11.

The introduction of lensed elements in the TLP 11 to straighten tiltedray bundles could be ideally in the form of a lensed face 23 to the TLP11; however, a separate lens and/or a lensed entrance to the LVF 2, arealso possible. With a cylindrical lens 23, e.g. 0.5 mm sag over a 6.4 mmactive area, using typical optical material, the tilted rays at the edgeof the detector array 3 can be straightened, which should recoveroptimal performance of the MicroNIR, e.g. linear wavelength spacing andoptimal resolution. See the taller and thinner plot in FIG. 8.

With reference to FIG. 9, a TLP boot 25 is provided for supporting theTLP 11, and functions to ensure that the reflected light from the sample15 is presented to the entrance aperture of the TLP 11 at the properacceptance angle defined by a first focal ratio, e.g. f/1 with a coneangle of about 30°, and that the field of view for the TLP 11 isdelivered to the LVF 2 at the required second focal ratio, e.g. f/3,with a cone angle of about 10°. The boot 25 includes a support section26, which supports at least the tip of the TLP 11 and ideally all of theTLP 11 without introducing strain, thereby protecting the TLP 11 fromshock and vibration. The boot 25 also includes a spacer section 27,which reduces the amount of the lamps 12 specular reflections from theprotective window 21 from reaching the entrance aperture of the TLP 11by recessing the TLP 11 and spacing the entrance end of the TLP 11 fromthe protective window 21. The spacer section 27 is in direct contactwith the entrance aperture of the TLP 11, and includes a plurality ofstepped inner surfaces 28, with a plurality of flat rectangular terraces29 with surfaces extending around the opening and perpendicular to thelongitudinal axis LA of the TLP 11, for reducing NIR light energy fromentering the TLP 11 at any other location, e.g. reflected from inputwindow. The side walls of the spacer section 27 converge in a step-wisemanner in length and width from the opening thereof to the opening ofthe TLP 11, which is disposed within the boot 25. If light does enterfrom other sites then the result is poor spectral performance of thesystem. The terraces 29 are analogous to focus bellows of the old platecameras, and are very effective at blocking and trapping unwantedscattered light from entering into the TLP 11. For the spectrometer 1,this enables higher OD measurements for transflectance measurements inaddition to better utilization of the detectors dynamic range.

If higher angle light flux enters into TLP 11 at the entrance aperturethe result is broadening of the spectral bandpass, secondary spectralpeaks, shoulders and pedestals on the spectral profile. The plots inFIGS. 10 a and 10 b illustrate the difference in a laser line spectralprofiles for a conventional boot (FIG. 10 a), and the boot 25 (FIG. 10b) of the present invention, which provides much higher resolution.

With reference to FIGS. 11 and 12, the LVF 2 of the present inventionreceives the collected light from the TLP 11 and transmits individualwavelength bands, which vary linearly across the length of the LVF 2 inascending or descending order. In the illustrated embodiment, the LVF 2comprises multi-layer stack with a spacer layer 30 between first andsecond reflector layers 31 and 32 on a substrate 33, as is well known inthe art. The first and second reflector layers 31 and 32 are depositedwith a tapering (converging or diverging) thickness in cross section,whereby the thicker the filter the longer the transmitted wavelength,The illustrated graph of % transmission vs wavelength includeswavelengths from 400 to 700; however, any range of wavelengths ispossible.

The center wavelength varies continuously along the length of the LVF 2,so the light hitting a detector pixel is the superposition of thebandwidths emanating from every point on the LVF 2 that the pixel can“see” (set by the F/# of the light). The center transmission wavelengthvaries linearly across the length of the LVF 2. In the example theextreme left end of the LVF 2 transmits a narrow range of bluewavelength only (shorter wavelength). As you move to the right thethickness of the LVF 2 increases and a longer wavelength is transmitted.Eventually at the extreme right only a narrow band of red light (longerwavelength) is transmitted.

The LVF 2 is designed to transmit a band of wavelengths at eachposition. The bands are designed to be comparable to, though usuallyless than, the total intended wavelength range divided by the number ofpixels. For example, in the existing spectrometer 1 with 128 pixels, theLVF 2 is designed to transmit a band of about 1% of the centralwavelength (10 nm at a center wavelength of 1000 nm). One of thestrengths of LVF technology is that the bands are not separated; inother words, every wavelength hitting the LVF 2 will be “seen” somewhereat the detector plane.

Instead of a power hungry and bulky cooling system, a temperaturefeedback device 41, e.g. thermistor, is ideally mounted in closeproximity to the detector array 3. The temperature-feedback device 41,can be either a thermistor, which changes resistance with temperature,or a precision IC, which outputs a known temperature-dependent voltage.The analog output of the temperature feedback device is read by thecontrol system 4 CPU. The control system 4 can then perform atemperature adjustment process to determine a temperature adjustedreading by accessing a look up table or formula stored in non-volatilememory that corrects the initial measurements based on the temperaturefrom the temperature feedback device.

The dark current and responsivity of the detector array 3 aretemperature dependent. Repeatable results are possible as long as thetemperature is stable; however, conventional wisdom is that thetemperature of the LVF 2 and detector array 3 should be as low aspossible.

In all applications, the gap between the LVF 2 and the detector array 3is set to minimize the spread of the beam of any wavelength emittingfrom the LVF 2; e.g. to optimize the beam spread to under three pixelson the detector array 3. An alternate embodiment would be to space thegap to ensure that the beam does not double in size between the LVF 2and the detector array 3.

FIG. 12 illustrates the importance of a small gap d between the LVF 2and the detector array 3. Assuming the light has the same cone, providedby the TLP 11, as the light hitting the LVF 2, i.e. f/3 or 9.59°, thespread S becomes d×tan 9.59°. For a gap d of 150 um, the spread becomes25 um. Accordingly, a single line on the LVF 2 creates a pixel-wide lineon the detector array 3.

For a gap of 150 um, every “line” of light emerging from the LVFdiverges at ±9.59°, creating a line ±25 um wide at the detector plane.This corresponds to the pixel pitch (50 um). Thus thewavelength-sensitive response of every line on the LVF 2 is split in aweighted fraction between two pixels. Accordingly, a gap less than 500um, preferably less than 200 um, and more preferably between 5 um and 80um, is preferred to minimize the optics required enabling the device tobe provided in a small package.

FIGS. 13 a and 13 b illustrate the difference in spectral performancefor a gap of 750 um (FIG. 10 a) and 200 um (FIG. 10 b), wherein thesmaller 200 um gap minimizes pixel cross talk, spectral broadening, andpedestals.

Ideally, the LVF 2 is as close to the detector array 3 as possible tomitigate spectral cross-talk between detector elements, as illustratedin FIG. 14. The best condition would be to directly attach the LVF 2 tothe pixels 52 of the detector array 3 using an optically transmissiveadhesive 51; however, the adhesive 51 also needs to: be electricallynon-conductive or dielectric in nature; be mechanically neutral byachieving good adhesion strength with inducing stress or destructiveforces to the detector array 3; optically compatible to transmit thedesired spectral content; remove reflection created at air to glassinterfaces; and have reasonable coefficient of thermal expansionproperties to minimize stress to the detector pixels 52 during curingand during thermal cycling. Accordingly, then the LVF 2 makes each pixel52 of the detector array 3 ideally respond to a different wavelength.

For example, the internal electronic components and wires 53 of thedetector array 3, e.g. an InGaAs linear diode array, are very sensitiveto any electrically conducting material, which will short out, damage ordestroy the detectors pixels or CMOS processing chip 54. An adhesivematerial 51 that mitigates this problem in this example is Epo-Tek353ND™, which is thermally curable not UV curable in nature. In thiscase thermally curable is acceptable, because the coating on the LVF 2,being directly attached to the pixels 52 on the detector array 3, willnot transmit UV energy. Moreover, EP 353ND (Clear or Black) hasexcellent dielectric properties before and after the curing process.Ideally, EP 353ND Clear can be used as the adhesive 51 between the LVF 2and the detector array 3 at a thickness of about 5 to 15 microns.

A “glass cover” 55, i.e. the substrate of the LVF 2 is provided over theLVF 2 covering most of the pixels 52 in the detector array 3, but notover the environmentally sensitive parts 53 of the sensor-bearing chip54. However, the adhesive EP 353ND also comes in an opaque, e.g. black,form that could be used as a potting agent 56 for the entire internalpackage. The opaque adhesive 56 would serve as an optical isolator orlight absorbing encapsulant or baffle, surrounding the LVF 2 andcovering the sensitive electrical components of the detector array 3,within the package to minimize stray light problems. The adhesivepotting agent 56 would also serve as an environmental protectant for theelectronics 53 within the package without the need of a cover window ascurrently required. Using the same material as the clear adhesive 51 andthe black potting material 56 has advantages thermally, optically and inmanufacturing.

Thus, there are three factors that affect the resolution (range ofwavelengths) that each pixel sees: first, the pixel width correspondsgeometrically to a range of center wavelengths on the LVF 2, forexample, a 50 um pixel with an LVF that ranges from 900-1700 nm sees 6.3nm of wavelength. Second, the LVF 2 has an innate bandwidth set by thecombination of design and cone angle of incident light (for example, 1%wide, or 9 nm to 17 nm, depending upon location). Third, the gap andcone angle impose a blurring or weighting effect (for example, 1 pixelwide, or an additional 6.3 nm, as a weighted average). It is thesuperposition of these that sets the overall resolution of theinstrument, e.g. in our current instrument, 1.1%.

Possible applications for the portable spectrometer 1 includein-the-field threat detection; identification and validation ofpharmaceuticals, controlled substances, and food products; forensics;process monitoring in the food industry (for example, moisture contentin grains); and identification of products for recycling andcontamination detection. Whatever has a near IR signal (structure) canbe measured and determined.

In an alternate embodiment, illustrated in FIG. 15, the handheld compactspectrometer 1 includes the optical package coupled to a battery-pack 59and a Bluetooth or WiFi chip 60 for communicating with the controllingdevice 7, e.g. control hardware and software, provided at remotelocations.

A user will be using the compact spectrometer 1 connected to an Android,Windows-based, or Apple iOS-based device, i.e. the controlling device 7,for real-time predictions. Ideally, the controlling device 7 and thecompact spectrometer 1 communicate via the USB cable 6 or a standaloneBluetooth or WiFi connection, i.e., they are the only two devices onthis local network. There is no cloud interface; the user would upload amethod file 62 or an app with a hardcoded method to non-transitorymemory of the controlling device 7, and the controlling device 7 isexpected to control the compact spectrometer 1 and execute the storedmethod file 62. The method file 62 refers to the combination ofpre-processing and spectral model(s) derived from a spectral library,which delivers a prediction to the end user of the compact spectrometer1. The method file 62 may contain more than one model if multipleresults are desired for the application. The method file 62 may alsoprescribe the desired compact spectrometer configuration, e.g. exposuretime, number of scans to average, or leave these settings to be definedas part of the instrument setup procedure.

Pre-processing are techniques of mathematical data treatment, orprocessing, to remove various effects in a set of the measured spectra,such as baseline offset or sample light scattering. Techniques includederivatives, scatter and baseline corrections. The specific choice ofpre-processing is chosen to enhance discrimination, i.e. to minimize thedifference between multiple spectra of the same material and maximizethe difference between spectra of dissimilar materials.

A spectral library is a series of spectral measurements of known“reference” materials, either a variety of different substances ormultiple versions of a single material type stored in non-transitorymemory on the controlling device 7 or a server 64 connected thereto.Examples might be a series of near infrared (NIR), infrared (IR) orRaman spectra of different samples of white powders. The spectrallibrary will be used to generate a ‘spectral model’.

A ‘spectral model’ refers to a mathematical equation derived from aspecific set of spectra. Models are typically regression vectors,derived statistically from the spectral library, which quantify thesimilarity of an unknown spectrum to those in the library. For example,a “spectral model” can include wavelengths, amplitudes, and widths ofspectral peaks corresponding to a given material. These wavelengths,amplitudes, and widths are compared to the wavelengths, amplitudes, andwidths of measured pre-processed spectra. The results of this comparisonmay be interpreted by a prediction engine 63 either qualitatively, forID or pass/fail applications, or quantitatively, for determination ofpurity or concentration.

The prediction engine is comprised of computer hardware and/or softwarestored in non-transitory memory on the controlling device 7. Thedetermined parameter or result is referred to as ‘prediction’. Theprediction provided by the prediction engine 63 can be transmitted tothe compact spectrometer 1 for the user to observe or simply observed onsuitable graphic user interface on the controlling device 7.Alternatively, the prediction can be stored in non-transitory memory onthe controlling device 7 or the remote server 64 for future review.

The prediction engine 63 may make predictions in one of two ways; first,simple methods using known models and pre-processing may be performeddirectly in the spectrometer provider software. Second, complex orthird-party-proprietary methods may be uploaded in a third-party format,and the controlling device 7 would communicate with a third-partyprediction “engine” to perform real-time predictions. The third-partyengine would need to be resident on the controlling device 7. Datareduction or projection techniques can include Partial Least Squares,Principle Component Analysis, Principle Component Regression, PartialLeast Square Discriminate Analysis, and Soft Independent Modeling ofClass Analogy.

Some users may wish to preserve a history of scans and predictions. Forthis purpose, the controlling device 7 will have the ability to savespectra and predictions locally and synchronize to a server 64 uponconnection to the network (for example, via USB, WiFi, Bluetooth or 4Gnetwork). The controlling device 7 will also have the ability to receiveupdated methods from the server 64 when synchronizing. Bar-code readerfor appropriate method selection may be desired in this scenario.

The method software 62 will have the ability to transmit unknown spectravia the server 64 to engineering for further evaluation or calibrationupdate.

In addition to storing and executing methods, the application method 62on the controlling device 7 will be able to set up and check the healthof the spectrometer 1, for example, perform reference measurements. The‘diagnostic’ capability of the compact spectrometer 1 will includemeasurement of an external wavelength accuracy standard (NIST 2036 orequivalent) and verification that the instrument accuracy is intact.Photometric noise and linearity calculations are also required. Thediagnostic scans can be done during initial start-up or upon userrequest.

In an alternate configuration, illustrated in FIG. 16, the compactspectrometer 1 and the controlling device 7 are connected to each otherand to a user's server 71 via a wireless network 72. An example of sucha system being a receiving dock at a pharmaceutical company. The methodfile 62 and the prediction engine 63 are stored on the server 71 insteadof the controlling device 7. In the infrastructure mode, the user willbe able (or even required) to scan a barcode 73 of the sample 15 to beanalyzed. The software stored in non-transitory memory and executed onthe controlling device 7 will use barcode recognition algorithms on aphoto taken with a camera on the controlling device 7, and use thebarcode 73 to select an appropriate method from the server 71, and labelthe recorded spectrum and result appropriately for display and storage.The user will then scan the material by pressing the integrated scanbutton of the compact spectrometer 1. The user may also want to commandthe scan from the controlling device 7. When the scan is complete, theuser will view the predicted result on the controlling device 7 andacknowledge the result based upon the method. If bar code integration isnot in effect at the user site, the user shall be able to select theappropriate method file from a list stored on the server 71 beforeperforming the spectral acquisition with the compact spectrometer 1.

In a special case within infrastructure mode, the operator may configurethe compact spectrometer 1, including selecting a method, and then carryjust the spectrometer 1 to scan samples in a single pass/failevaluation. In this mode, the spectrometer 1 will communicate with thecontrolling device 7 and via the WAN 72, be triggered by the integratedscan button, and provide audible, visual or tactile (vibratory) feedbackas to pass/fail results.

The methods, spectra and results will all be saved/stored on the userdatabase server 71, not on the controlling device 7. Additionally,methods may be executed on the local cloud, i.e. the server 71, with theresult passed back to the controlling device 7, which are transparent tothe user. A user with appropriate privileges should have the ability toview results from multiple compact spectrometers 1 and offer privilegemanagement for multiple users, e.g. the ability to generate or only usemethods, by interacting with the local cloud. 21 CFR Part 11 compliantsoftware is required for this scenario, as such; each user shall havedifferent ‘administrative’ privileges allowing trained operators to onlyuse the compact spectrometer 1 as they are allowed. 21 CFR Part 11 alsoprovides a mechanism for data authenticity, where no data can be deletedor altered without appropriate authority. The local server 71 isexpected to be an integral part of 21CFR Part 11 compliance.

In yet another configuration, which is highly specific to theapplication of the compact spectrometer 1, the core architecture ofcloud-based computing is critical. The core architecture and themeasurement process is similar to that depicted in FIG. 17.

The user for this configuration is a novice and does not necessarilyhave experience with NIR technology or the spectrometer 1. The user ismerely looking for the spectrometer 1 to provide an answer based on avery specific sampling and testing procedure. The typical jargon is“standard operating procedure,” or SOP. A law enforcement officer, ahazmat technician, or military personnel are good examples.

A sophisticated app on the controlling device 7 will guide the userthrough initialization and configuration of the compact spectrometer 1.The app will download updates and methods, as needed, from thespectrometer provider's server 71 disposed in a remote and securelocation, e.g. via one or more networks, such as the internet, andreport diagnostics back to the spectrometer provider's server 71. Inthis configuration, the option of fully characterizing and periodicallyverifying the instrument to the point that baseline and zero would nolonger have to be performed in the field and setup would be completelyautomatic, is provided.

In “Cloud-Based Operation mode”, the spectrometer provider's personnelwill be responsible for managing method software 62 and monitoringsystem health and performance. The method software 62 will be owned andmanaged by the provider of the spectrometer 1. As such, any updates tothe method software 62 will need to be ‘pushed’ to the local subscriberbase.

Similarly, results and data generated by the spectrometer 1 will berelayed back to the server 71 of the spectrometer provider (or theirpartner), and archived for possible future use. The data coming back tothe spectrometer provider server 71 from the end user's samples 15 willbe screened for statistical similarity or uniqueness based upon both theresults from the field and upon further analysis of uploaded spectra bymethods applied at the spectrometer provider server 71. If the sample isdeemed unique when compared to the spectrometer provider's library, thespectrum will be flagged as a possible addition to the future methodupdate (and the user will be notified and requested to provide moreinformation). In essence, this is collecting unique samples for futureinclusion to the model to account for any variability not currentlyaddressed by the existing method.

We claim:
 1. A portable spectrometer device comprising: an illuminationsource for directing light at a sample; a tapered light pipe (TLP) forcapturing light interacted with the sample at a first focal ratio andfor delivering the light at a second focal ratio lower than the firstfocal ratio; a linearly variable filter (LVF) for separating thecaptured light into a spectrum of constituent wavelength signals; and adetector array, including a plurality of pixels, each of the pluralityof pixels disposed to receive at least a portion of one of theconstituent wavelength signals providing a power reading for eachconstituent wavelength; wherein the TLP includes a first smaller end forpositioning adjacent to the sample, a second wider and taller endadjacent to the LVF, and sidewalls diverging from the first end to thesecond end for mixing and spreading the light across the LVF.
 2. Thedevice according to claim 1, wherein the TLP accepts light at the firstfocal ratio of f/1 with a cone angle of between 20° and 40°, anddelivers the reflected light to the LVF with second focal ratio slowerthan f/3 with a cone angle of less than 10°.
 3. The device according toclaim 1, wherein the TLP includes a lensed exit face for straighteningtilted ray bundles for delivery to the LVF.
 4. The device according toclaim 1, wherein the LVF and the detector array are separated by a gapof less than 200 um, for increasing spectral resolution.
 5. The deviceaccording to claim 4, wherein the gap ensures that a single line on theLVF creates a pixel-wide line on the detector array.
 6. The deviceaccording to claim 4, wherein the LVF is bonded directly to the detectorarray; and wherein the gap comprises an optically transparent adhesive 5to 15 microns thick.
 7. The device according to claim 1, furthercomprising a TLP boot including a support section for supporting theTLP, and a spacer section for spacing the TLP from the sample ensuringthat the light from the sample is presented to the TLP at a desiredacceptance angle defined by the first focal ratio f/1 with a cone angleof about 30°.
 8. The device according to claim 7, wherein the spacersection of the TLP boot includes stepped inner walls for reducingspecular reflections from reaching the TLP.
 9. The device according toclaim 1, further comprising a housing; and a control system within thehousing, the control system comprised of a processor, a suitablenon-transitory memory, and a USB connector for receiving a USB cord,enabling the transfer of data between the processor and a host computer.10. The device according to claim 1, further comprising a Bluetooth orWIFI chip for communicating with a controlling device, which sends testsprocedures and receives test results.
 11. The device according to claim1, further comprising a battery or a USB cable connector for providingthe spectrometer with less than 2.5 W of power.
 12. The device accordingto claim 1, further comprising a housing for enclosing the illuminationsource, the TLP, the LVF and the detector array, wherein the housing isless than 2″×2″.
 13. The device according to claim 12, wherein thehousing, the illumination source, the TLP, the LVF and the detectorarray weigh less than 0.5 pounds.
 14. The device according to claim 1,wherein the illumination source comprises at least one light source,disposed at an acute angle from the longitudinal axis of the LVF, forgenerating a spot on the sample, whereby light is reflected from thesample along the longitudinal axis into the LVF.
 15. The deviceaccording to claim 14, wherein each light source comprises a lens tippedvacuum tungsten lamp for creating a less than 5 mm spot on the sample.16. The device according to claim 14, wherein the illumination sourcecomprises two light sources; and wherein an end of the TLP is disposedbetween the two light sources.
 17. The device according to claim 1,further comprising a temperature feedback system for adjusting the powerreading of each constituent wavelength based on an ambient temperature.18. A spectrometer system comprising: the portable spectrometer deviceof claim 1; a controlling device operably coupled to the portablespectrometer for controlling the portable spectrometer; and a serveroperably coupled to the handheld spectrometer and the controlling devicevia a wireless digital network for storing spectrums.
 19. The systemaccording to claim 18, wherein the controlling device is configured toreceive the spectrum from the handheld spectrometer; to compare thespectrum to a library of spectrums; and to output a result of thecomparison to a display.
 20. The system according to claim 18, whereinthe server is configured to receive the spectrum from the handheldspectrometer; to compare the spectrum to a library of spectrum models;and to output a result of the comparison to a display.
 21. Thespectrometric system of claim 20, wherein the server includes a store ofscan characteristics and spectrum models; wherein the controlling deviceincludes a barcode reader, wherein in operation, the barcode readerreads a barcode corresponding to the sample, the controlling devicecommunicates the barcode to the server, and the server selects the scancharacteristics and spectrum models for comparison based on the barcode.